Switched mode power supplies are pervasive in the electronics field because of their ability to efficiently convert a first DC or AC voltage to a second regulated output level. Such power supplies are used, for example, in computer power supplies, DC power adapters, and automotive power supplies. As the demand for low power, low cost electronics have increased, a corresponding need for low cost systems and methods of switched mode power supplies has resulted.
One barrier to more efficient switched-mode power supplies has been transient ringing due to switching current in the transformer. The efficiency of a power converter is partially determined by the amount of switching loss in the transformer. This switching loss is directly proportional to the frequency of the converter. The presence of the transient ringing, however, causes mistriggering of the switching transistor, which can result in a significant increase in the system switching frequency. Mistriggering of a switch transistor due to transient ringing is disadvantageous because the resulting increased switching frequency leads to inefficient power supply performance, increased electromagnetic interference (EMI), and poor load regulation.
To address the issue of transient ringing, some conventional power supply systems have imposed a fixed turn-off time for current switches coupled to magnetic components within the power supply. Because of the wide tolerance of parts used within many power supplies, however, these fixed turn-off times are often designed to last considerably longer than a nominally expected transient. Increased turn-off time lowers the maximum realizable output power of the power supply.
In the field of switched-mode power supplies, what is needed are cost effective and power efficient systems and methods for switched-mode power supplies.